702 



Figure 1 shows their thermoelectric forces against copper, at the 

 absohite temperature T, given in the first column of the table. The 

 temperature of the second juncture was 16° C. 



^ 3. Cliange of the resistance of alloys with temperature. As it 

 appeared impossible to find a suitable thermo-couple, our attention 

 was drawn to the change of resistance of constantin, \yhich had 

 already been measured at hydrogen temperatures by Kaimerlingh 

 Onnes and Clay. This alloy shows here a considerable decrease 

 of resistance at decreasing temperature; it was, therefore, probable 

 that constantin could be suitably used as a resistance thermometer at 

 helium temperatures. Experiments have shown that this was in fact 

 the case. Later measurements (see comm. N". 142r/ §4) proved that 

 also manganin, whose resistance begins to diminish at decreasing 

 temperature and wdiich has at oxygen temperatures a considerable 

 smaller resistance than at ordinary temperatures, is fit for tempera- 

 ture measurements in liquid helium. 



§ 4. Specif c heat of mercury, a. Experimental arrangements. 



The method, used in the determination of the specific heat, 

 agrees most with the one used by Nernst in his investigations 

 about the specific heat. A little block of solid mercury hung freely in 

 a high vacuum and was heated electrically. The increase of temperature 

 was determined by means of a constantin resistance thermometer. 

 To obtain the little block of mercury the liquid metal (comp. fig. 2 

 with magnified fig. of details) was poured into the vessel C through 

 a capillary, provided with a funnel, which could be introduced 

 through m. First C was in the same way supplied by means of a 

 funnel with a small quantity of pure pentane, which, at the intro- 

 duction of the mercury, remains as a thin layer between the glass 

 and the mercury. A little hollow steel cylinder (thickness of the 

 wall 7^0 m.m.), which contained the heating wire — a constantin 

 wire, insulated with silk and covered with a thin layer of celluloid 

 to avoid all electrical contact with the mercury — was immersed 

 in the mercury. Round this cylinder a second constantin wire was 

 wrapped, which was to be used as a thermometer. The little cy- 

 linder was, by means of silk wires (stiffened by celluloidj fixed to 

 a little glass rod, which could be moved up and down through 

 the tube .6, and which was centred by constrictions in this tube. 

 This glass rod was connected to a silk wire, which could be 

 screwed up and down by turning the handle K. Now the mercury 

 was frozen by cooling down to the temperature of liquid air. The 



